1. Field of the Invention
The present invention relates to earphones and devices using the earphones. More particularly, the present invention relates to a compatible circuit and method for 4- and 5-pole earphones and to a portable device using the same.
2. Description of the Related Art
In recent years, portable devices have been designed to provide a variety of functions in addition to the voice communication function. For example, portable devices now often include a file reproduction function for reproduction of audio and video files, a camera function for photographing a picture or a moving image, a Push To Talk (PTT) function, etc.
The PTT function is a communication service in which, after Internet Protocol (IP) addresses are allocated to respective portable devices, the portable device are able to wirelessly communicate with each other in a one-to-one mode or in a one-to-multi mode using an IP network, without using a mobile communication service network. The PTT function is a means of instantaneous communication commonly employed in radio transceivers in which a push-button is pushed in to select a voice transmission mode and the push-button is released to select a voice reception mode, thereby allowing the devices to be operated in a bi-directional communication mode. This type of radio communication allows a speaker to hear several people simultaneously and allows transmission and reception to be performed through a single frequency band. That is, the PTT service allows a user to communicate with others in a one-to-one mode or in a one-to-multi mode by operating a PTT key. Moreover, the PTT key may be mounted in a portable device or in an earphone coupled to the portable device.
The conventional portable devices that include a PTT function have been employing a 5-pole earphone as the standard. The 5-pole earphone is used, rather than a 4-pole earphone, because it includes an additional pole or terminal for detecting the PTT key. Notably, the 5-pole earphone has an interface unit that has the same physical size as the interface unit of a 4-pole stereo earphone (hereinafter referred to as a 4-pole earphone). Therefore, users may insert a 4-pole earphone plug into a portable device that is designed to use the 5-pole earphone. However, since the pin map is different between the 4- and 5-pole earphones, a portable device designed to employ a 5-pole earphone has difficulty using a 4-pole earphone. More specifically, if a 4-pole earphone plug is inserted into the 5-pole earphone jack of the portable device, a microphone associated with the 4-pole earphone may work normally but the right speaker of the earphone outputs the left audio sound of the stereo and the left speaker outputs a reduced right audio sound. The resulting output may confuse the user into believing that the portable device, designed to be used for a 5-pole earphone, or the 4-pole earphone has malfunctioned.
Once again, these problems are caused because the earphone interface unit of the portable device employing a 5-pole earphone has a different pin map than that of a 4-pole earphone. That is, the pin map differs between the 4- and 5-pole earphones. Therefore, depending on the type of earphone plug connected to the portable device, a circuit is required to adapt to the pin map of the earphone interface unit. To this end, a circuit is needed to detect the type of earphone connected to the portable device and a switching circuit is required to switch the path of an audio signal according to the detected type of earphone.
A circuit is also needed to make a portable device using a 5-pole earphone to recognize the operation of a PTT key.